Thursday, March 13, 2008

Danger Bearings

It is possible to keep a ship in safe water without frequent fixes through the use of danger bearings. The figure above shows a shoal that presents a hazard to navigation, a prominent landmark at point A, and a ship proceeding along the coastline on course BC. To construct a danger bearing, line AX is drawn from point A tangent to the outer edge of the danger. If the bearing of point A remains greater than the danger bearing, the ship is in safe water, as with YA and ZA. The reverse is true when the danger is to port, the danger angle must remain greater than the angle to point A.
Wind or current could set the ship toward the shoal. However, even before a fix could be taken, this situation would be indicated by repeated bearings of point A.